/** @file
  Simple wrapper functions and utility functions that access QEMU's modern CPU
  hotplug register block.

  These functions manipulate some of the registers described in
  "docs/specs/acpi_cpu_hotplug.txt" in the QEMU source. IO Ports are accessed
  via EFI_MM_CPU_IO_PROTOCOL. If a protocol call fails, these functions don't
  return.

  Copyright (c) 2020, Red Hat, Inc.

  SPDX-License-Identifier: BSD-2-Clause-Patent
**/

#include <IndustryStandard/Q35MchIch9.h>     // ICH9_CPU_HOTPLUG_BASE
#include <IndustryStandard/QemuCpuHotplug.h> // QEMU_CPUHP_R_CMD_DATA2
#include <Library/BaseLib.h>                 // CpuDeadLoop()
#include <Library/DebugLib.h>                // DEBUG()

#include "QemuCpuhp.h"

UINT32
QemuCpuhpReadCommandData2 (
  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo
  )
{
  UINT32     CommandData2;
  EFI_STATUS Status;

  CommandData2 = 0;
  Status = MmCpuIo->Io.Read (
                         MmCpuIo,
                         MM_IO_UINT32,
                         ICH9_CPU_HOTPLUG_BASE + QEMU_CPUHP_R_CMD_DATA2,
                         1,
                         &CommandData2
                         );
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a: %r\n", __FUNCTION__, Status));
    ASSERT (FALSE);
    CpuDeadLoop ();
  }
  return CommandData2;
}

UINT8
QemuCpuhpReadCpuStatus (
  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo
  )
{
  UINT8      CpuStatus;
  EFI_STATUS Status;

  CpuStatus = 0;
  Status = MmCpuIo->Io.Read (
                         MmCpuIo,
                         MM_IO_UINT8,
                         ICH9_CPU_HOTPLUG_BASE + QEMU_CPUHP_R_CPU_STAT,
                         1,
                         &CpuStatus
                         );
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a: %r\n", __FUNCTION__, Status));
    ASSERT (FALSE);
    CpuDeadLoop ();
  }
  return CpuStatus;
}

UINT32
QemuCpuhpReadCommandData (
  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo
  )
{
  UINT32     CommandData;
  EFI_STATUS Status;

  CommandData = 0;
  Status = MmCpuIo->Io.Read (
                         MmCpuIo,
                         MM_IO_UINT32,
                         ICH9_CPU_HOTPLUG_BASE + QEMU_CPUHP_RW_CMD_DATA,
                         1,
                         &CommandData
                         );
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a: %r\n", __FUNCTION__, Status));
    ASSERT (FALSE);
    CpuDeadLoop ();
  }
  return CommandData;
}

VOID
QemuCpuhpWriteCpuSelector (
  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo,
  IN UINT32                       Selector
  )
{
  EFI_STATUS Status;

  Status = MmCpuIo->Io.Write (
                         MmCpuIo,
                         MM_IO_UINT32,
                         ICH9_CPU_HOTPLUG_BASE + QEMU_CPUHP_W_CPU_SEL,
                         1,
                         &Selector
                         );
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a: %r\n", __FUNCTION__, Status));
    ASSERT (FALSE);
    CpuDeadLoop ();
  }
}

VOID
QemuCpuhpWriteCommand (
  IN CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo,
  IN UINT8                        Command
  )
{
  EFI_STATUS Status;

  Status = MmCpuIo->Io.Write (
                         MmCpuIo,
                         MM_IO_UINT8,
                         ICH9_CPU_HOTPLUG_BASE + QEMU_CPUHP_W_CMD,
                         1,
                         &Command
                         );
  if (EFI_ERROR (Status)) {
    DEBUG ((DEBUG_ERROR, "%a: %r\n", __FUNCTION__, Status));
    ASSERT (FALSE);
    CpuDeadLoop ();
  }
}

/**
  Collect the APIC IDs of
  - the CPUs that have been hot-plugged,
  - the CPUs that are about to be hot-unplugged.

  This function only scans for events -- it does not modify them -- in the
  hotplug registers.

  On error, the contents of the output parameters are undefined.

  @param[in] MmCpuIo           The EFI_MM_CPU_IO_PROTOCOL instance for
                               accessing IO Ports.

  @param[in] PossibleCpuCount  The number of possible CPUs in the system. Must
                               be positive.

  @param[in] ApicIdCount       The number of elements each one of the
                               PluggedApicIds and ToUnplugApicIds arrays can
                               accommodate. Must be positive.

  @param[out] PluggedApicIds   The APIC IDs of the CPUs that have been
                               hot-plugged.

  @param[out] PluggedCount     The number of filled-in APIC IDs in
                               PluggedApicIds.

  @param[out] ToUnplugApicIds  The APIC IDs of the CPUs that are about to be
                               hot-unplugged.

  @param[out] ToUnplugCount    The number of filled-in APIC IDs in
                               ToUnplugApicIds.

  @retval EFI_INVALID_PARAMETER  PossibleCpuCount is zero, or ApicIdCount is
                                 zero.

  @retval EFI_PROTOCOL_ERROR     Invalid bitmap detected in the
                                 QEMU_CPUHP_R_CPU_STAT register.

  @retval EFI_BUFFER_TOO_SMALL   There was an attempt to place more than
                                 ApicIdCount APIC IDs into one of the
                                 PluggedApicIds and ToUnplugApicIds arrays.

  @retval EFI_SUCCESS            Output parameters have been set successfully.
**/
EFI_STATUS
QemuCpuhpCollectApicIds (
  IN  CONST EFI_MM_CPU_IO_PROTOCOL *MmCpuIo,
  IN  UINT32                       PossibleCpuCount,
  IN  UINT32                       ApicIdCount,
  OUT APIC_ID                      *PluggedApicIds,
  OUT UINT32                       *PluggedCount,
  OUT APIC_ID                      *ToUnplugApicIds,
  OUT UINT32                       *ToUnplugCount
  )
{
  UINT32 CurrentSelector;

  if (PossibleCpuCount == 0 || ApicIdCount == 0) {
    return EFI_INVALID_PARAMETER;
  }

  *PluggedCount = 0;
  *ToUnplugCount = 0;

  CurrentSelector = 0;
  do {
    UINT32  PendingSelector;
    UINT8   CpuStatus;
    APIC_ID *ExtendIds;
    UINT32  *ExtendCount;
    APIC_ID NewApicId;

    //
    // Write CurrentSelector (which is valid) to the CPU selector register.
    // Consequences:
    //
    // - Other register accesses will be permitted.
    //
    // - The QEMU_CPUHP_CMD_GET_PENDING command will start scanning for a CPU
    //   with pending events at CurrentSelector (inclusive).
    //
    QemuCpuhpWriteCpuSelector (MmCpuIo, CurrentSelector);
    //
    // Write the QEMU_CPUHP_CMD_GET_PENDING command. Consequences
    // (independently of each other):
    //
    // - If there is a CPU with pending events, starting at CurrentSelector
    //   (inclusive), the CPU selector will be updated to that CPU. Note that
    //   the scanning in QEMU may wrap around, because we must never clear the
    //   event bits.
    //
    // - The QEMU_CPUHP_RW_CMD_DATA register will return the (possibly updated)
    //   CPU selector value.
    //
    QemuCpuhpWriteCommand (MmCpuIo, QEMU_CPUHP_CMD_GET_PENDING);
    PendingSelector = QemuCpuhpReadCommandData (MmCpuIo);
    if (PendingSelector < CurrentSelector) {
      DEBUG ((DEBUG_VERBOSE, "%a: CurrentSelector=%u PendingSelector=%u: "
        "wrap-around\n", __FUNCTION__, CurrentSelector, PendingSelector));
      break;
    }
    CurrentSelector = PendingSelector;

    //
    // Check the known status / event bits for the currently selected CPU.
    //
    CpuStatus = QemuCpuhpReadCpuStatus (MmCpuIo);
    if ((CpuStatus & QEMU_CPUHP_STAT_INSERT) != 0) {
      //
      // The "insert" event guarantees the "enabled" status; plus it excludes
      // the "remove" event.
      //
      if ((CpuStatus & QEMU_CPUHP_STAT_ENABLED) == 0 ||
          (CpuStatus & QEMU_CPUHP_STAT_REMOVE) != 0) {
        DEBUG ((DEBUG_ERROR, "%a: CurrentSelector=%u CpuStatus=0x%x: "
          "inconsistent CPU status\n", __FUNCTION__, CurrentSelector,
          CpuStatus));
        return EFI_PROTOCOL_ERROR;
      }

      DEBUG ((DEBUG_VERBOSE, "%a: CurrentSelector=%u: insert\n", __FUNCTION__,
        CurrentSelector));

      ExtendIds   = PluggedApicIds;
      ExtendCount = PluggedCount;
    } else if ((CpuStatus & QEMU_CPUHP_STAT_REMOVE) != 0) {
      DEBUG ((DEBUG_VERBOSE, "%a: CurrentSelector=%u: remove\n", __FUNCTION__,
        CurrentSelector));

      ExtendIds   = ToUnplugApicIds;
      ExtendCount = ToUnplugCount;
    } else {
      DEBUG ((DEBUG_VERBOSE, "%a: CurrentSelector=%u: no event\n",
        __FUNCTION__, CurrentSelector));
      break;
    }

    //
    // Save the APIC ID of the CPU with the pending event, to the corresponding
    // APIC ID array.
    //
    if (*ExtendCount == ApicIdCount) {
      DEBUG ((DEBUG_ERROR, "%a: APIC ID array too small\n", __FUNCTION__));
      return EFI_BUFFER_TOO_SMALL;
    }
    QemuCpuhpWriteCommand (MmCpuIo, QEMU_CPUHP_CMD_GET_ARCH_ID);
    NewApicId = QemuCpuhpReadCommandData (MmCpuIo);
    DEBUG ((DEBUG_VERBOSE, "%a: ApicId=" FMT_APIC_ID "\n", __FUNCTION__,
      NewApicId));
    ExtendIds[(*ExtendCount)++] = NewApicId;

    //
    // We've processed the CPU with (known) pending events, but we must never
    // clear events. Therefore we need to advance past this CPU manually;
    // otherwise, QEMU_CPUHP_CMD_GET_PENDING would stick to the currently
    // selected CPU.
    //
    CurrentSelector++;
  } while (CurrentSelector < PossibleCpuCount);

  DEBUG ((DEBUG_VERBOSE, "%a: PluggedCount=%u ToUnplugCount=%u\n",
    __FUNCTION__, *PluggedCount, *ToUnplugCount));
  return EFI_SUCCESS;
}
